It is common practice to provide means for applying a retarding force to a shaft or other rotating part of a machine, to compensate for looseness caused by wear. Such slack in the power transmission system tends to create "chatter", and to produce inaccuracy when machining operatives are involved. In some instances, for example, as much as two degrees of backlash can result from gear train wear when the working load upon tooling is relieved, and the attendant problems may be particularly acute in those instances in which small tools, which must be handled with considerable delicacy, are involved. Although many different forms of machines suffer from difficulties of this nature, those in which constant and frequent indexing occurs, such as in automatic screw machines, represent specific instances in which it is particularly important to damp spurious movement caused by wear.
As indicated, this has been accomplished in the past by creating a drag upon a shaft of the machine, developed by frictional force that is applied either continuously or intermittently. The former approach is disadvantageous for a number of reasons, including the need that it creates for overpowering of the machine, so as to ensure the availability of sufficient net energy for providing the desired speed and other characteristics of operation; also, there is of course a substantial waste of energy and the generation of excessive amounts of heat.
Other forms of devices apply the retarding force only during the working phase of the cycle, relieving it when indexing is to occur. While offering obvious advantages over constant-drag arrangement, the prior art systems of this type have typically relied upon springs or hydraulic and pneumatic means to effect the dynamic action required; furthermore, they have not been entirely satisfactory in operation, and they have tended to be overly complex and prone to premature failure.
The foregoing and other deficiencies of the prior art devices have been at least substantially overcome in the brake assembly and related subject matter of the aboveidentified copending application. As described therein, however, the "floating" clevis is provided with a pin which is so disposed as to engage a structural part of the machine, to thereby prevent inadvertent disassembly when the machine is backed up. It has been found that such a manner of interengagement tends to rotate the clevis about the axis of the actuating arm, thereby causing a tightening force to be exerted upon the brake band. The force developed often makes manual reversal of the machine quite difficult, and can in fact be of such magnitude as to virtually arrest reversal.
Accordingly, it is the broad object of the present invention to provide a novel mount, usually in the form of a clevis, having a hooking portion for engaging a stationary member to prevent disassembly upon reverse action of the machine in which it is installed, without however imposing undue restraint upon movement of the machine components.
Related objects are to provide a novel mechanical brake assembly, and a novel machine combination, in which the mount is incorporated.
Another object is to provide such a mount which is of relatively uncomplicated and inexpensive construction, and which is nevertheless highly effective for its intended purposes.